A gas sensor is set up to determine the concentration of a predetermined gas, for example ozone, in a fluid medium such as air. For this purpose, the gas sensor follows the indirect measuring principle, in which a gas-sensitive element is provided, on which it is possible to determine a parameter that can be influenced by the gas concentration. Ideally, the parameter depends only on the concentration of the gas to be measured (selectivity). Even small changes in the gas concentration are intended to measurably influence the parameter (sensitivity). There should be a defined relationship between the gas concentration and the measurable parameter (accuracy). The property to be measured should change as quickly as possible with the gas concentration (short measuring time). In addition, these changes should be reversible (service life of the sensor). The concentration should be measurable with little outlay (costs and ability to be miniaturized) and the measurement method should need only little energy, in order to be suitable for mobile application, for example in a Smartphone.
A small and indirectly measuring gas sensor is usually based on a field effect transistor (FET) or a metal oxide layer (MOX layer). In the FET-based sensors, the gas to be measured normally influences the work function of a gas-sensitive layer applied to the gate electrode and therefore normally causes a change in the source-drain current. Examples of such sensors are described in the applications DE 10 2008 048 715 or EP 1 104 884 82.
In the gas sensors which are based on an MOX layer, the electrical resistance of a heatable MOX layer is measured. This resistance changes as a result of the presence of specific gases and their chemical interaction with the MOX layer (oxidation and reduction processes). In order to control the sensitivity and selectivity of the sensor for a predetermined gas, the MOX layer can be heatable. By means of thermal stimulation, the sensor can be kept in a defined state in order to ensure the desired measuring accuracy. The thermal stimulation is also called regeneration. Other types of regeneration are likewise possible, for example optical.